Apple is planning to build a solar farm near its massive $1 billion data center complex in North Carolina, The Charlotte Observer reported.

Apple has been rather mum over the years about clean energy unlike other companies that have publicly shared their "greener" data centers such as Google and Yahoo. So it's not surprising there are so few details yet on the solar farm. Here's what we know.

The permits issued by Catawba County show Apple has been given the OK to reshape the slope of about 170 acres of vacant land across from its planned data center given the once-secret code name of Project Dolphin, The Observer reported. Apple purchased that land in July 2009. At the time, it wasn't clear what Apple would use the land for, Apple Insider reported. Although some speculated it would be used for more data center or even office space.

Aside from the plans' name, Project Dolphin Solar Farm A Expanded, there are few details. There's no information on what company will develop the solar farm, what tech that will be used or the project's size.

The company has been criticized in the past for its lack of clean energy-sourced power and a lack of transparency in its operations. Apple does provide some information about its environmental footprint, including it recycling and the amount of greenhouse gas emission its products produce. According to Apple, the company's facilities in Austin, Texas; Sacramento, Calif.; and Cork, Ireland are 100 percent powered by renewable energy. However, the company doesn't provide specific details about how it achieves this.

Plenty of companies are tinkering with ways to make data centers more efficient while keeping servers cool. And for good reason: Data centers use a lot of electricity, mainly to cool servers. In the U.S. alone, data centers account for about 1.5 percent of electricity usage, according to the EPA.

Last year, Yahoo unveiled an unconventional data center designed like a chicken coop to use outdoor air for cooling. Google jumped headfirst into data center innovations, going so far as to share with everyday IT folk some of its data center efficiency secrets. Earlier this year, Google revealed its seawater-cooled data center in Finland. And then there's green data center start-up Power Assure. which makes software that ties its power consumption to server usage. Meaning, when Internet traffic drops off at night, the software dials down power consumption and vice versa.

Kirsten Korosec has written for Technology Review, Marketing News, The Hill, BNET and Bloomberg News. She holds a degree from Northwestern University's Medill School of Journalism. She is based in Tucson, Arizona.
Follow her on Twitter.